On Tue, Nov 15, 2011 at 03:00:09AM +0100, Andrea Arcangeli wrote: > On Mon, Nov 14, 2011 at 04:03:45PM -0800, Andrew Morton wrote: > > On Fri, 11 Nov 2011 10:01:56 +0000 > > Mel Gorman <mgorman@xxxxxxx> wrote: > > > A 1000-hour compute job will have its pages collapsed into hugepages by > > > khugepaged so they might not have the huge pages at the very beginning > > > but they get them. With khugepaged in place, there should be no need for > > > an additional tuneable. > > > > OK... > > It's good idea to keep it monitored. But I guess the reduced rate will > only materialize at temporary VM stress times. > > > Fair enough. One slight problem though: > > > > akpm:/usr/src/25> grep -r thp_collapse_alloc_failed Documentation > > akpm:/usr/src/25> > > I didn't fill that gap but I was reading the code again and I don't > see why we keep retrying for -EAGAIN in the !sync case. Maybe the > below is good (untested). I doubt it's good to spend cpu to retry the > trylock or to retry the migrate on a pinned page by O_DIRECT. The retry happens on the expectation that the page is not locked for very long. Pinning for O_DIRECT would be an exception. Readahead pages would be another. I don't have data on how often we encounter a page that is locked for a very short period of time versus being locked for IO and even if I did, it would be depend on the workload and the amount of RAM. > In fact > as far as THP success rate is concerned maybe we should "goto out" > instead of "goto fail" but I didn't change to that as compaction even > if it fails a subpage may still be successful at creating order > 1/2/3/4...8 pages. I only avoid 9 loops to retry a trylock or a page > under O_DIRECT. Maybe that will save a bit of CPU, I doubt it can > decrease the success rate in any significant way. I'll test it at the > next build... > > ==== > From: Andrea Arcangeli <aarcange@xxxxxxxxxx> > Subject: [PATCH] migrate: !sync don't retry > > For !sync it's not worth retrying because we won't lock_page even > after the second pass. Except in the cases where the page was locked for a very short period of time. I think this will have an impact on success rates for minimal latency savings but I cannot predict how much of an impact. -- Mel Gorman SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>